Thomas Rücker

Okay, found it. 
Problem was not the 21:9, but rather the very low and strange resolution the game was set on the beginning.
Felt strange having to modify a .json file (%apdata%/roaming/vintagestorydata/clientsettings.json) to set the correct resolution, but at least now it works correctly  even in ultrawide (3440x1440).

(and no, it did not use the desktop resolution, somewhat more of 1/6 of my desktop resolution for width, and half of that for the height)

How can i change the resolution? (display resolution, not 3d scale resolution)

There is no resolution slider in the game like in 100% of other games!

The main problem is that i have an ultrawide display, and with a resolution of 3440x1440 the game looks crappy, and often menus (at least the lower buttons) are halfway or fully cut off and unsee and unclickable. So i would like to change the game resolution to a normal 16:9 instead of the 21:9 scale, like i do with other problematic games that don't support ultrawide correctly.